The present invention pertains to a process for producing ozone for the treatment of materials, according to which process the ozone is produced from oxygen in an ozone generator.
Ozone is an excellent oxidant for many organic and inorganic compounds. It is possible, for example, to treat undesirable components present in water to discolor or detoxify them or to render them biodegradable or flocculable. The oxidizing effect of ozone is utilized in chemistry, e.g., to produce acid. Pulp is bleached with ozone. The surface of plastics can be modified by ozone treatment. Gases can also be reacted with ozone; for example, nitric oxide can be oxidized with ozone.
For industrial applications, ozone is produced in ozone generators by silent electric discharge from air or pure oxygen. Since only part of the oxygen fed into the ozone generator is transformed into ozone, the nonconverted oxygen must be separated from the ozone and recycled into the ozone generator in the case of ozone generation from pure oxygen for economic reasons. This oxygen separation can be carried out in pressure swing absorbers. The ozone is adsorbed by silica gel in these plants during the adsorption phase under slightly increased pressure. The ozone is subsequently desorbed under a somewhat lower pressure during a desorption phase. A scavenging gas is used for the desorption; however, it has the disadvantage of diluting the desorbed ozone.
A process in which the desorption is carried out under lower than atmospheric pressure is known from DE-OS No. 32 30 922. The vacuum is generated, e.g., by a water jet gas compressor. The ozone is drawn off from the pressure swing adsorber without dilution and is mixed with the water of the water jet gas compressor. the ozone can undergo the intended reactions even in this water, if so desired.
It has been found in connection with the practical application of the process according to DE-OS No. 32 30 922 that the ozone concentration in the desorbed gas is not constant during the desorption process. A high concentration peak appears at the beginning of the desorption process, and the ozone concentration decreases continuously during the desorption. In addition, a considerable pressure rise occurs in the desorption pipe at the beginning of the desorption phase, especially when the vacuum applied is low and the volume of the desorption pipe is small.
The fluctuations in concentration are caused by the decreasing ozone loading of the silica gel during the desorption phase. The concentration is also influenced by residual oxygen which has been adsorbed in the silica gel and in the free and pore volumes of the silica gel adsorber during the adsorption process, because it is also present in the desorbed gas. Such variations in concentration and pressure are irrelevant for many applications. However, they can have an adverse effect on the intended reactions with ozone when the reaction and hold times are short.